1. Field of the Invention
The invention relates to the field of radio frequency amplifiers, particularly those which are bidirectional or bilinear.
2. Prior Art
Radio frequency transceivers often employ manually operated means for switching between transmitting and receiving modes. Such switching is used to prevent the high power output of the transceiver from being coupled into the receiver, in addition to other uses.
In applications where a bidirectional power amplifier is employed in the antenna line of the transceiver additional complexity is required to couple the transmit/receive switching signal from the manually operated button to the bidirectional amplifier. This additional complexity is particularly troublesome where the transceiver is remotely located from the antenna. In this situation a bidirectional amplifier (for amplifying both the transmitted signal and received signal) may be located close to the antenna to amplify the small received signal before it is attenuated in the long line between the transceiver and antenna. Also by amplifying the transmitted signal at the antenna, power loss in the long lines is reduced.
In the prior art, the transmit/receive switching has been done automatically with a relay, or the like. A portion of the transmitted carrier signal is rectified and used to operate the relay. When the carrier signal is not present, the relay automatically switches the antenna to the receiver. One problem with this technique is that there is a switching time dalay and moreover, large signals received by the antenna (which could damage the receiver) are coupled to the receiver. As will be seen, the present invention solves this problem in a unique and simple manner, without the use of relays, and without the need to rectify the transmitted signal.